The invention relates to a method of appropriately prevent thermal spalling caused in the refractory.
It is known that the refractory bricks or various kinds of ceramic products for the installation of the steel making furnaces create the thermal spalling by rapid difference in temperature.
With respect to the thermal spalling, when the refractory product is effected with the difference in temperature, free deformation at each of the parts composing the product is restrained owing to the differences of the materials of the parts or the difference in the amount of thermal expansion by the difference in temperature, and the thermal spalling is a phenomenon cracking the product when the thermal stress by the restrain of the deformation reaches enough to bring about destruction of the product.
For dealing with the thermal spalling, there have been proposed many countermeasures, for example, a method of decreasing the change of temperature given to the product, a method of employing such materials having high thermal shock resistance, or a method of heat treatment at the softening temperature of making the temperature of the product uniform, as seen in the reinforced glass, and forcedly cooling its surface for imparting the residual stress of compression to the surface. However, the first method has the problems of taking long period of the operating time and difficult in controlling the temperature. The second method is economically disadvantageous and may be involved with the problem of other physical characteristics, and this is not always useful. The third method has difficulties of providing the residual stress to the sintered substance unlike the glass, and in addition, the distribution of the residual stress is such that the surface is of compression and the inside is of corresponding tension, and if the product is a thin plate it is strong to the thermal spalling but if it has other shapes than the plate it does not work usefully.
The present invention has been realized in view these circumstances through experiments and investigations.
It is the first object of the invention to provide a method of remarkably improving the spalling resistance of the ceramic product to be used in the furnaces. It is the second object of the invention to provide a method of elongating the service life of the ceramic product by improving the spalling resistance with the aim of stabilization in long term of operation. It is the third object of the invention to provide a method of preventing the thermal spalling, which may be put into practice at low cost for many refractory bricks.
Other objects and features of the invention will be apparent from the following description of the invention in reference to the attached drawings.